1. FIELD OF THE INVENTION
The present invention relates to a seat belt system, particularly to a passive seat belt system which automatically causes a seat belt to move between a fitted position, in which the occupant is restricted by means of the seat belt, and a release position, in which the occupant is not restricted by means of the seat belt, when the occupant is getting in and out of a vehicle.
2. DESCRIPTION OF THE PRIOR ART
The Japanese Patent First Publication Showa 56-71643 discloses a passive seat belt system. In this system, a guide rail is mounted on the roof side rail of a vehicle. A sliding block, which is slidable on the guide rail, is provided at one end of a seat belt. The sliding block is connected to one end of an actuation wire and the other end of the actuation wire is drivingly associated with a drive motor for driving the sliding block along the guide rail. Therefore, one end of the seat belt can move along the guide rail according to the movement of the sliding block which is driven by the drive motor via the actuation wire. In addition, a latch base is provided at one end of the guide rail on the side of the drive motor, i.e. at the rear end of the guide rail. When the sliding block is moved from the front end of the guide rail, i.e. the release position, to the position of the latch base, i.e. the fitted position, an engaging portion, which is provided at the tip of the sliding block, is latched by means of the latch base. The movement of the sliding block is completed at this position, so that the occupant is restricted by means of the seat belt.
The movement of the sliding block is controlled by a control circuit which includes a door switch and two limit switches. The door switch comprises two stationary terminals and a movable contact which is movable between the stationary terminals in accordance with opening and closing of the door. One of the stationary terminals, to which the movable contact contacts while the door is opened, will be hereafter referred to as "door open position detecting terminal". The other stationary terminal, to which the movable contact contacts while the door is closed, will be hereafter referred to as "door closed position detecting terminal".
One of the limit switches is oriented adjacent the front end of the guide rail for detecting the sliding block at the front end. This limit switch will be thus referred as "front end position detecting switch". The other limit switch is positioned adjacent the rear end of the guide rail for detecting the sliding block at the rear end. This limit switch is thus referred to as "rear end position detecting switch". In addition, the control circuit includes a sensor which becomes ON to restrict the movement of the sliding block when the vehicle is rapidly decelerated, such as upon collision of the vehicle.
In order to assure emergency safety operation of the seat belt, inspection has to be performed after installation of the seat belt system to the vehicle or after completion of assembling of the vehicle. A difficulty of inspection is encountered. Normally, unless emergency condition, such as collision, occurs to cause rapid deceleration of the vehicle, the sensor will be held OFF to maintain the seat belt system at initial position. On the other hand, when the connection between the sensor and the control circuit is broken, no trigger signal to actuate the seat belt system will be input to hold the seat belt system at the initial. position. Therefore, inspection has to be performed under emergency condition in which the seat belt system becomes active when the sensor is connected. In practice, to turn the sensor ON, substantial deceleration has to be applied to the vehicle. This requires substantially high skill in checking emergency seat belt locking condition.